The present invention relates to an electrophotographic processor, such as a laser beam printer, a copier, a plain paper facsimile, etc., and more particularly, to a heating roller apparatus of a fixing unit for permanently fixing a toner image transferred onto a recording medium.
The electrophotographic printing process requires an image fixing procedure to fuse a toner image onto a receiving surface of a recording medium, such as paper, or the like. A typical image fixing unit comprises a heating roller and a pressure roller between which the recording medium passes. Various image fixing units for electrophotographic printing devices are disclosed in prior art; see, for example, U.S Pat. Nos. 4,933,724 and 5,115,279.
Several common problems exist with conventional image fixing units. One of these problems is the lack of temperature uniformity along the surface of the heating roller during the electrophotographic printing process. This problem, if severe enough, can result in the generation of printed copies which are defective. Another problem associated with conventional image fixing units is a prolonged delay time when warming up to perform an electrophotographic printing process. While this problem can be mitigated to a certain extent by simply maintaining the temperature of the heating roller at a predetermined temperature during non-printing periods, this solution has a disadvantage in that it consumes an unnecessary amount of electrical power.